The use of solid state light emitting devices (LEDs) for conventional lighting applications, such as vehicle light bulbs, interior and exterior lighting, and so on, continues to increase, due primarily to their expected useful life, and their efficiency. In these applications, the production of white light is often a requirement.
To produce white light, or any light that differs in color from the color produced inherently from a given light emitting material, a color shift and color combination is generally used to achieve the desired color, or, with regard to while light, the desired color temperature. A color shift (wavelength conversion) can be provided by materials, such as phosphors, that absorb light of one color and emit light of a different color. Typically, a layer of material that contains phosphor particles is applied upon the upper surface of the light emitting device. As the light exits the light emitting device and enters the phosphor layer, some or all of the emitted light strike the phosphor particles, such that the light output from the phosphor layer comprises a combination of the original emitted light and the subsequently produced converted light. The composite color output will be dependent upon the proportion of light at each wavelength (color), which is dependent primarily upon the density and distribution of the phosphor particles.
To reduce manufacturing costs, the phosphor layer is applied to a wafer of fabricated light emitting elements (dies). After applying the phosphor layer, the wafer is sliced/diced to provide the individual/singulated light emitting elements. Generally, a laser-based process is preferred for dicing the wafer into individual light emitting elements; however, the phosphor layer can be damaged if exposed to laser energy. Accordingly, mechanical processes are used for dicing phosphor coated wafers.
A disadvantage of having to mechanically dice phosphor coated wafers is that the kerf width of a saw is typically in the order of 50-100 um, which is substantially wider than the typical kerf width of a laser cut, typically in the order of 10-15 um. In order to allow for this wider kerf width and the manufacturing tolerances, the individual light emitting elements must be spaced farther apart, by 200 um or more, reducing the number of light emitting elements that can be fabricated on each wafer. For example, if the light emitting element is 500 um×500 um, and the dicing lane width, often called a “street”, between light emitting elements is 200 um, only about 36% of the available wafer area will be used for the light emitting elements, compared to almost 90% wafer area utilization for non phosphor coated light emitting elements using laser slicing with a 30 um street.